Particle-optical apparatuses use beams of charged particles, such as electron beams and ion beams, for example, for many different purposes, e.g. for obtaining information about objects and for structuring objects. By way of example, electron beam and ion beam microscopes are used to obtain information about examined materials, and electron beam lithography appliances, electron beam welding appliances and ion beam appliances are used to modify the structure of objects.
In a particle beam system, one or more particle beams are produced by a particle source and directed onto an object. To this end, it is desirable to influence the particle beams in a targeted manner using suitable particle-optical apparatuses in order, for example, to direct the particle beams in focus onto a desired location at the object. Such particle-optical apparatuses use magnetic and/or electric fields for influencing the particle beams. The spatial dependence and symmetry of the produced fields is determined by the geometry of the electrodes or coils used to produce the electric and magnetic fields. The spatial dependence and symmetry of the fields determines how the particle-optical apparatus influences the particle beams passing through the fields. By way of example, there are particle-optical apparatuses which provide fields that act as lenses in order to change the convergence of a particle beam passing through the apparatus, there are apparatuses that act as a beam deflector in order to deflect a particle beam passing through the apparatus through a desired angle and there are e.g. apparatuses that act as stigmators in order to astigmatically influence a particle beam passing through the apparatus.
A particle-optical system may be put together from a multiplicity of such apparatuses in order to successively influence the one or more particle beams in different ways, wherein some of the apparatuses also serve to set or adjust the beam within the system in such a way that the beam enters into a subsequent apparatus in a desired way. Here, the design of a particle-optical system is subject to boundary conditions which are predetermined, inter alia, by the installation space assumed by the electrodes and coils, and the holding structures thereof, used to produce the fields. Therefore, in general, it is not possible to realize all desired spatial dependencies and symmetries of fields for influencing the particle beams for a certain desired particle beam system as only a reasonable number of particle-optical apparatuses are available for influencing the particle beams.